Magnetic structures, methods of forming the same and memory devices including a magnetic structure

ABSTRACT

Magnetic structures, methods of forming the same, and memory devices including a magnetic structure, include a magnetic layer, and a stress-inducing layer on a first surface of the magnetic layer, a non-magnetic layer on a second surface of the magnetic layer. The stress-inducing layer is configured to induce a compressive stress in the magnetic layer. The magnetic layer has a lattice structure compressively strained due to the stress-inducing layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority from Korean PatentApplication No. 10-2012-0002041, filed on Jan. 6, 2012, in the KoreanIntellectual Property Office, the disclosure of which is incorporatedherein by reference in its entirety.

BACKGROUND

1. Field

Example embodiments relate to magnetic structures, methods of formingthe same, and memory devices including a magnetic structure.

2. Description of the Related Art

Magnetic random access memories (MRAMs) are memory devices that storedata by using a variation in resistance of a magnetic tunneling junction(MTJ) element of a memory cell. The resistance of the MTJ element variesaccording to a magnetization direction of a free layer. That is, whenthe magnetization direction of the free layer is the same as amagnetization direction of a pinned layer, the MTJ element has lowresistance. When the magnetization direction of the free layer isopposite to the magnetization direction of the pinned layer, the MTJelement has high resistance. A case where the MTJ element has the lowresistance may correspond to data ‘0’, and a case where the MTJ elementhas the high resistance may correspond to data ‘1’. Because such a MRAMis non-volatile is capable of high speed operations and has highendurance, the MRAM has gained attention as one of the next generationnon-volatile memory devices.

In order to increase a recording density of MRAM (i.e., to obtain a highdensity MRAM), a size of the MTJ element has to be reduced. However,when the size of the MTJ element is reduced, thermal stability of datarecorded in a data storage layer (i.e., free layer) decreases. Thus,securing a data retention characteristic becomes difficult. In thisregard, it is not easy to increase the recording density of the MRAMover a certain level.

SUMMARY

Example embodiments relate to magnetic structures, methods of formingthe same, and memory devices including a magnetic structure.

Provided are magnetic structures suitable for scaling downmagnetoresistive elements.

Provided are magnetic structures capable of increasing magneticanisotropy energy of a magnetic layer.

Provided are magnetic structures capable of increasing thermal stabilityof a magnetic layer.

Provided are magnetic structures capable of increasing a criticalthickness for maintaining perpendicular magnetic anisotropy of amagnetic layer.

Provided are magnetic structures capable of increasing amagnetoresistance ratio (i.e., a MR ratio).

Provided are magnetic structures suitable for realizing high density andhigh performance of a memory device.

Provided are methods of forming a magnetic structure.

Provided are memory devices including the magnetic structures.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

According to example embodiments, a magnetic structure may include amagnetic layer, a stress-inducing layer on a first surface of themagnetic layer, and a non-magnetic layer on a second surface of themagnetic layer, wherein the stress-inducing layer is configured toinduce a compressive stress in the magnetic layer, and the magneticlayer has a lattice structure compressively strained due to thestress-inducing layer.

The magnetic layer may have interface perpendicular magnetic anisotropy(IPMA) due to an interface between the magnetic layer and thenon-magnetic layer.

The magnetic layer may include a Fe-based material or a CoFe-basedmaterial. The CoFe-based material may include CoFeB.

The non-magnetic layer may include an insulating material. Thenon-magnetic layer may include an oxide. The oxide may include amagnesium (Mg) oxide, for example.

The stress-inducing layer may include a material with a thermalexpansion coefficient higher than a thermal expansion coefficient of themagnetic layer.

The stress-inducing layer may include at least one of Al, Ga, Mn, Zn,Cu, and combinations thereof, for example.

The stress-inducing layer may include a phase transformation material.

The stress-inducing layer may include a material with a latticeparameter smaller than a lattice parameter of the magnetic layer.

The magnetic layer may be between the stress-inducing layer and thenon-magnetic layer.

The magnetic layer may include a first layer in contact with thenon-magnetic layer, and a second layer between the first layer and thestress-inducing layer.

A saturation magnetization (Ms) of the second layer may be smaller thana saturation magnetization of the first layer.

When the magnetic layer includes the first layer and the second layer,the magnetic layer may have a thickness of about 1 nm to about 3 nm.

The first layer may have a thickness of about 1 nm or less.

The second layer may have a thickness of about 2 nm or less.

The magnetic layer may be a first magnetic layer. The magnetic structuremay include a second magnetic layer on a surface of the non-magneticlayer. The non-magnetic layer may be disposed between the first magneticlayer and the second magnetic layer.

One of the first and second magnetic layers may be a free layer, and theother may be a pinned layer.

The magnetic structure may be a magnetoresistive element.

According to example embodiments, a method of forming a magneticstructure may include forming a magnetic layer having a latticestructure compressively strained due to a stress-inducing layer, andforming a non-magnetic layer contacting the magnetic layer.

The magnetic layer may have interface perpendicular magnetic anisotropy(IPMA) due to an interface between the magnetic layer and thenon-magnetic layer.

The stress-inducing layer may be formed of a material with a thermalexpansion coefficient higher than a thermal expansion coefficient of themagnetic layer.

When the stress-inducing layer is formed the material with the thermalexpansion coefficient higher than the thermal expansion coefficient ofthe magnetic layer, forming the magnetic layer may include heating thestress-inducing layer, forming a magnetic material layer on the heatedstress-inducing layer, and cooling the magnetic material layer and thestress-inducing layer such that the lattice structure of the magneticmaterial layer is compressively strained.

When the stress-inducing layer is formed the material with the thermalexpansion coefficient higher than the thermal expansion coefficient ofthe magnetic layer, forming the magnetic layer may include heating themagnetic material layer, forming the stress-inducing layer on the heatedmagnetic material layer, and cooling the stress-inducing layer and themagnetic material layer such that the lattice structure of the magneticmaterial layer is compressively strained.

The stress-inducing layer may be formed of a phase transformationmaterial.

When the stress-inducing layer is formed of a phase transformationmaterial, forming the magnetic layer may include forming thestress-inducing layer and a magnetic material layer in contact with thestress-inducing layer; and changing a phase of the stress-inducing layersuch that the lattice structure of the magnetic material layer may becompressively strained.

The stress-inducing layer may be formed of a material with a latticeparameter smaller than a lattice parameter of the magnetic layer.

The magnetic layer may be formed including a first layer in contact withthe non-magnetic layer, and a second layer disposed between the firstlayer and the stress-inducing layer, wherein a saturation magnetization(Ms) of the second layer may be smaller than a saturation magnetizationof the first layer.

The magnetic layer may be a first magnetic layer. The method may furtherinclude forming a second magnetic layer on a surface of the non-magneticlayer, and the non-magnetic layer may be disposed between the first andsecond magnetic layer.

One of the first and second magnetic layers may be a free layer, and theother may be a pinned layer.

According to example embodiments, a memory device includes at least onememory cell including a magnetoresistive element, wherein themagnetoresistive element includes first and second magnetic layersspaced apart from each other, a non-magnetic layer between the first andsecond magnetic layers, and a stress-inducing layer configured to inducea compressive stress in the first magnetic layer, wherein the firstmagnetic layer has a lattice structure compressively strained due to thestress-inducing layer.

The memory cell may further include a switching element connected to themagnetoresistive element.

The first magnetic layer may be a free layer, and the second magneticlayer may be a pinned layer.

The first magnetic layer may have interface perpendicular magneticanisotropy (IPMA) due to at an interface between the first magneticlayer and the non-magnetic layer.

The stress-inducing layer may include a material with a thermalexpansion coefficient higher than a thermal expansion coefficient of thefirst magnetic layer.

The stress-inducing layer may include a phase transformation material.

The stress-inducing layer may include a material with a latticeparameter smaller than a lattice parameter of the first magnetic layer.

The first magnetic layer may include a first layer in contact with thenon-magnetic layer, and a second layer disposed between the first layerand the stress-inducing layer, wherein a saturation magnetization (Ms)of the second layer may be smaller than a saturation magnetization ofthe first layer.

The memory device may be a magnetic random access memory (MRAM).

The memory device may be a spin transfer torque magnetic random accessmemory (STT-MRAM).

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings of which:

FIGS. 1 through 4 are cross-sectional views of magnetic structuresaccording to example embodiments;

FIGS. 5 through 8 are cross-sectional views of magnetoresistive elementsincluding magnetic structures according to example embodiments;

FIGS. 9A through 9E are cross-sectional views showing a method offorming a magnetic structure (a magnetoresistive element) according toexample embodiments;

FIG. 10 is a flowchart summarizing a method of forming the magneticstructure of FIGS. 9A through 9E;

FIGS. 11A through 11D are cross-sectional views showing a method offorming a magnetic structure (a magnetoresistive element) according toexample embodiments;

FIG. 12 is a flowchart summarizing a method of forming the magneticstructure of FIGS. 11A through 11D;

FIGS. 13A through 13D are cross-sectional views showing a method offorming a magnetic structure (a magnetoresistive element) according toexample embodiments;

FIG. 14 is a flowchart summarizing a method of forming the magneticstructure of FIGS. 13A through 13D;

FIGS. 15A through 15C are cross-sectional views showing a method offorming a magnetic structure (a magnetoresistive element) according toexample embodiments;

FIG. 16 is a flowchart summarizing a method of forming the magneticstructure of FIGS. 15A through 15C;

FIG. 17 is a drawing illustrating an example of a memory deviceincluding a magnetic structure (a magnetoresistive element) according toexample embodiments;

FIG. 18(A) is a drawing showing a crystalline structure of MgO/Fe;

FIG. 18(B) is a graph showing a change in a surface magnetic anisotropyenergy (K_(S)) according to a lattice parameter of Fe in a structure ofMgO/Fe;

FIG. 19(A) is a drawing showing a crystalline structure of MgO/CoFe;

FIG. 19(B) is a graph showing a change in a surface magnetic anisotropyenergy (K_(S)) of a lattice parameter of CoFe in a structure ofMgO/CoFe; and

FIGS. 20A and 20B are drawings respectively showing a first phase(ε′-phase) and a second phase (τ-phase) of MnAl which may correspond toa stress-inducing layer material of a magnetic structure according toexample embodiments.

DETAILED DESCRIPTION

Various example embodiments will now be described more fully withreference to the accompanying drawings in which example embodiments areshown.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. As used herein the term “and/or” includesany and all combinations of one or more of the associated listed items.

It will be understood that, although the terms “first”, “second”, etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another element, component, region, layer or section. Thus,a first element, component, region, layer or section discussed belowcould be termed a second element, component, region, layer or sectionwithout departing from the teachings of the example embodiments.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to (an) other element(s)or feature(s) as illustrated in the figures. It will be understood thatthe spatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting of theexample embodiments. As used herein, the singular forms “a,” “an” and“the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. It will be further understood thatthe terms “comprises” and/or “comprising,” when used in thisspecification, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

Example embodiments are described herein with reference tocross-sectional illustrations that are schematic illustrations ofidealized embodiments (and intermediate structures) of exampleembodiments. As such, variations in the shapes of the illustrations as aresult, for example, of manufacturing techniques and/or tolerances, areto be expected. Thus, the example embodiments should not be construed aslimited to the particular shapes of regions illustrated herein but areto include deviations in shapes that result, for example, frommanufacturing. For example, an implanted region illustrated as arectangle will, typically, have rounded or curved features and/or agradient of implant concentration at its edges rather than a binarychange from implanted to non-implanted region. Likewise, a buried regionformed by implantation may result in some implantation in the regionbetween the buried region and the surface through which the implantationtakes place. Thus, the regions illustrated in the figures are schematicin nature and their shapes are not intended to illustrate the actualshape of a region of a device and are not intended to limit the scope ofthe example embodiments.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which example embodiments belong. Itwill be further understood that terms, such as those defined incommonly-used dictionaries, should be interpreted as having a meaningthat is consistent with their meaning in the context of the relevant artand will not be interpreted in an idealized or overly formal senseunless expressly so defined herein.

Expressions such as “at least one of,” when preceding a list ofelements, modify the entire list of elements and do not modify theindividual elements of the list.

In the drawings, the thicknesses of layers and regions are exaggeratedfor clarity. Like reference numerals in the drawings denote likeelements.

Example embodiments relate to magnetic structures, methods of formingthe same, and memory devices including a magnetic structure.

FIG. 1 is a cross-sectional view of a magnetic structure according toexample embodiments.

Referring to FIG. 1, a non-magnetic layer N10 may be formed on a surface(e.g., a lower surface) of a magnetic layer M10. A stress-inducing layerS10 may be formed on another surface (e.g., an upper surface) of themagnetic layer M10. The magnetic layer M10 may have an interfaceperpendicular magnetic anisotropy (IPMA) property due to an interface(i.e., a contact surface) between the magnetic layer M10 and thenon-magnetic layer N10. That is, the magnetic layer M10 and thenon-magnetic layer N10 may constitute an IPMA system or an IPMAstructure. The magnetic layer M10 may include a Fe-based material or aCoFe-based material. Here, the Co—Fe-based material may include, forexample, CoFeB. The non-magnetic layer N10 may be an insulating layer.In this case, the non-magnetic layer N10 may include an oxide. The oxidemay include, for example, a magnesium oxide (i.e., MgO). Although CoFeB,which is mentioned for a material of the magnetic layer M10, normally(intrinsically) have an in-plane magnetic anisotropy (IMA) property,when CoFeB is in contact with a given oxide (e.g., MgO), CoFeB may havea perpendicular magnetic anisotropy (PMA) property due to an interfacialeffect. A thickness of the magnetic layer M10 may be equal to or lessthan about 2 nm, and a thickness of the non-magnetic layer N10 may beequal to or less than about 3 nm. However, the thicknesses of themagnetic layer M10 and the non-magnetic layer N10 are not limitedthereto and may vary.

The stress-inducing layer S10 may be a layer inducing a compressivestress in the magnetic layer M10. In other words, the stress-inducinglayer S10 may apply a compressive stress to the magnetic layer M10. Thecompressive stress is a compressive stress in the in-plane direction.The magnetic layer M10 may have a lattice structure that iscompressively strained due to the stress-inducing layer S10. That themagnetic layer M10 is compressively strained means that the magneticlayer M10 has a lattice parameter smaller than that of an equilibriumstate (i.e., unstrained state) thereof. Because the magnetic layer M10is thin, the lattice structure of all region of the magnetic layer M10may be compressively strained. That is, as well as a region of themagnetic layer M10 which is in contact with the stress-inducing layerS10, the opposite region (i.e., a region of the magnetic layer M10 whichis in contact with the non-magnetic layer N10) may also be compressivelystrained. When the magnetic layer M10 has a compressively strainedstructure, magnetic anisotropy energy of the magnetic layer M10 mayincrease. In other words, the magnetic layer M10 may have a highermagnetic anisotropy energy when the magnetic layer M10 is compressivelystrained than when the magnetic layer M10 is not compressively strained(e.g., when the magnetic layer M10 is in an equilibrium state). When themagnetic layer M10 has IPMA due to the interface with the non-magneticlayer N10, the magnetic anisotropy energy of the magnetic layer M10 maybe referred to as “a surface magnetic anisotropy energy (K_(S)).”Therefore, the surface magnetic anisotropy energy K_(S) of the magneticlayer M10 may increase due to the stress-inducing layer S10. As themagnetic anisotropy energy of the magnetic layer M10 increases, thermalstability of magnetization of the magnetic layer M10 may be increased,which will be described later in detail.

The stress-inducing layer S10 may include a material with a thermalexpansion coefficient greater than that of the magnetic layer M10. Thematerial with a thermal expansion coefficient greater than that of themagnetic layer M10 may be, for example, Al, Ga, Mn, Zn, Cu orcombinations thereof. A thermal expansion coefficient of Al is aboutdouble that of Fe, and a thermal expansion coefficient of Ga is aboutten times greater than that of Fe. Although a layer, for example an Allayer, including the material with a thermal expansion coefficientgreater than that of the magnetic layer M10 is in contact with themagnetic layer M10, the Al layer may not induce stress in the magneticlayer M10 if the Al layer is not formed under certain conditions. If theAl layer is formed under the certain conditions, the Al layer may be alayer inducing stress in the magnetic layer M10, that is, may be thestress-inducing layer S10. Therefore, not just any layer formed of Al,Ga, Mn, Zn, Cu or combinations thereof may correspond to thestress-inducing layer S10. A method of forming the stress-inducing layerS10 using the material with a thermal expansion coefficient greater thanthat of the magnetic layer M10 will be described later in detail.

According to example embodiments, the stress-inducing layer S10 mayinclude a phase transformation material. The phase transformationmaterial may be a material that has a first phase at low temperature andhas a second phase at high temperature. A lattice parameter of thesecond phase in the in-plane direction may be smaller than that of thefirst phase. Thus, as a crystalline structure of the phasetransformation material transforms from the first phase to the secondphase, a compressive stress may be induced in the magnetic layer M10.The phase transformation material may be a material which transforms tothe second phase at high temperature and continuously maintains thesecond phase even when the temperature is decreased to low temperature.That is, the phase transformation material may be a material thattransforms its phase irreversibly. For example, the phase transformationmaterial may include MnAl. A method of forming the stress-inducing layerS10 using the phase transformation material will be described later indetail. According to example embodiments, the stress-inducing layer S10may include a material with a lattice parameter smaller than that of themagnetic layer M10. The lattice parameter of the stress-inducing layerS10 in the in-plane direction may be smaller than that of the magneticlayer M10. A difference between the lattice parameter of thestress-inducing layer S10 and the lattice parameter of the magneticlayer M10 may be within about 10%. If the material with the latticeparameter smaller than that of the magnetic layer M10 is in contact withthe magnetic layer M10, compressive stress may be induced in themagnetic layer M10. Meanwhile, although a thickness of thestress-inducing layer S10 is not particularly limited, the thickness maybe less than or equal to about 20 nm.

As mentioned above, as the magnetic layer M10 is compressively strained,the magnetic anisotropy energy of the magnetic layer M10 may beincreased. The reason for this will be described with reference to FIGS.18 and 19.

Drawing (A) of FIG. 18 shows a crystalline structure of MgO/Fe, anddrawing (B) shows a change in the surface magnetic anisotropy energy(K_(S)) according to the lattice parameter of Fe in the structure ofMgO/Fe. Drawing (A) of FIG. 19 shows a crystalline structure ofMgO/CoFe, and drawing (B) shows a change in the surface magneticanisotropy energy (K_(S)) according to the lattice parameter of CoFe inthe structure of MgO/CoFe. Here, the lattice parameter is a latticeparameter between Fe atoms (i.e., Fe—Fe) in the in-plane direction, andthe surface magnetic anisotropy energy (K_(S)) is an intrinsic surfaceperpendicular magnetic anisotropy energy (intrinsic K_(S)). Meanwhile,CoFe of FIG. 19 is Co_(0.4)Fe_(0.6).

Referring to FIGS. 18 and 19, as the lattice parameters of Fe and CoFebecoming smaller than that of the equilibrium state (2.95 Å), thesurface magnetic anisotropy energy (K_(S)) has a tendency to beincreased. This indicates that in a case where a magnetic layer is Fe orCoFe based, when the magnetic layer has a lattice parameter smaller thanthat of an equilibrium state (i.e., when the magnetic layer has alattice structure that is compressively strained), the surface magneticanisotropy energy (K_(S)) increases. Particularly, when the latticeparameter of CoFe in FIG. 19 is about 2.65 Å, the surface magneticanisotropy energy (K_(S)) shows a very high value of about 6 erg/cm².

For the same reason explained with reference to FIGS. 18 and 19, whenthe magnetic layer M10 of FIG. 1 has a compressively strainedcrystalline structure, its magnetic anisotropy energy or surfacemagnetic anisotropy energy may be increased. In this regard, the thermalstability of magnetization of the magnetic layer M10 may be improved.The thermal stability of a magnetic layer (e.g., M10 of FIG. 1) in theIPMA structure is proportional to a ratio of the magnetic anisotropyenergy and a thermal energy (i.e., K_(S)A/k_(B)T). Here, ‘K_(S)’represents the surface magnetic anisotropy energy (erg/cm²) of themagnetic layer, ‘A’ represents a surface area of the magnetic layer (acontact surface area in contact with a non-magnetic layer), ‘k_(B)’represents a Boltzmann constant, and ‘T’ represents absolutetemperature. Depending on how large the magnetic anisotropy energy(K_(S)A) is in comparison with the thermal energy (k_(B)T), the thermalstability of the magnetic layer may be determined. Therefore, as thesurface magnetic anisotropy energy (K_(S)) increases, the thermalstability may be improved. According to example embodiments, as themagnetic anisotropy energy (K_(S)) increases due to the stress-inducinglayer S10, the thermal stability of the magnetic layer M10 may be easilysecured. This means that it is easy to reduce the size of the magneticlayer M10. In other words, scaling down of the magnetic layer M10 ispossible without adverse effects. If the surface magnetic anisotropyenergy (K_(S)) of the magnetic layer M10 is high, a value of themagnetic anisotropy energy (K_(S)A) may be maintained high even when asize (width) of the magnetic layer M10 is reduced. According to exampleembodiments, scaling down to 20 nm or less may be possible, and thusultra high density devices may be manufactured.

The structure of FIG. 1 is merely exemplary, and the structure may bechanged in various ways. For example, although FIG. 1 illustrates a casewhere the magnetic layer M10 and the stress-inducing layer S10 aresequentially stacked on the non-magnetic layer N10, their relation interms of location may be changed. A changed example is illustrated inFIG. 2.

Referring to FIG. 2, the stress-inducing layer S10 may be formed on thelower surface of the magnetic layer M10, and the non-magnetic layer N10may be formed on the upper layer of the magnetic layer M10. That is, themagnetic layer M10 and the non-magnetic layer N10 may be sequentiallystacked on the stress-inducing layer S10. Materials, properties,thicknesses, etc. of the magnetic layer M10, the stress-inducing layerS10, and the non-magnetic layer N10 may be the same as those describedwith reference to FIG. 1.

FIG. 3 is a cross-sectional view of a magnetic structure according toexample embodiments.

Referring to FIG. 3, a magnetic layer M11 may have a multi-layerstructure. For example, the magnetic layer M11 may have a double-layerstructure including a first layer 10 and a second layer 20. The firstlayer 10 may be formed of the same material as the magnetic layer M10 ofFIG. 1. That is, the first layer 10 may include a material that isFe-based or CoFe-based. Here, the CoFe-based material may include, forexample, CoFeB. The first layer 10 may have IPMA at an interface with anon-magnetic layer N10. Due to the first layer 10, all of the magneticlayer M11 may have perpendicular magnetic anisotropy (PMA). That is, themagnetic isotropy of the magnetic layer M11 may be determined by thefirst layer 10. The second layer 20 may be formed of a material withsaturation magnetization (Ms) smaller than that of the first layer 10.For example, the second layer 20 may have a composition in which anon-magnetic material is added to a given magnetic material. Thenon-magnetic material may serve to reduce the saturation magnetization(Ms) of the second layer 20. The magnetic material of the second layer20 may include at least one of Co, Fe, and Ni, and the non-magneticmaterial may include, for example, V, Al, Cr, Ti, Ta or combinationsthereof. A thickness of the first layer 10 may be, for example, about 1nm or less, and a thickness of the second layer 20 may be, for example,about 2 nm or less. An entire thickness of the magnetic layer M11 may beabout 3 nm or less, for example about 1 to 3 nm. As such, if themagnetic layer M11 is constructed in the multi-layer structure, acritical thickness of the magnetic layer M11, of which PMA or IPMA ismaintained, may be increased. The following is a detailed explanation.

When the thickness of the magnetic layer M10 is excessively thickened,IPMA of the magnetic layer M10 may not be maintained because if themagnetic layer M10 has a large thickness, demagnetization energy becomesgreater than the perpendicular magnetic anisotropy energy due to aninterfacial effect between the magnetic layer M10 and the non-magneticlayer N10. Therefore, when the thickness of the magnetic layer M10 islarge, magnetic anisotropy may change from perpendicular to in-plane.The following Equation 1 shows a relationship between an intrinsicsurface perpendicular magnetic anisotropy energy (intrinsic K_(S)) andan effective surface perpendicular magnetic anisotropy energy (effectiveK_(S)).

Effective K _(S)=Intrinsic K _(S)−2π·Ms ² ·t  Equation 1

In Equation 1, 2π·Ms²·t represents a demagnetization energy. As thethickness (t) of the magnetic layer M10 is increased in FIG. 1, thedemagnetization energy increases and the effective surface perpendicularmagnetic anisotropy energy (effective K_(S)) decreases. Therefore, whenthe thickness (t) reaches a certain level or higher, the magneticanisotropy of the magnetic layer M10 may change from perpendicular toin-plane. In this regard, it may be difficult to increase the thickness(t) of the magnetic layer M10 in the structure of FIG. 1.

However, as in the example embodiments of FIG. 3, when the second layer20 having a low saturation magnetization Ms is used, saturationmagnetization Ms of the entire magnetic layer M11 may be lowered, andthus the demagnetization energy may be lowered. Thus, a criticalthickness of the magnetic layer M11, of which IPMA is maintained, may beincreased. Therefore, the thickness of the magnetic layer M11 may beincreased to 1 nm or more. For example, the thickness of the magneticlayer M11 may be about 1 to 3 nm, or about 1.5 to 3 nm. When amagnetoresistive element is formed using the magnetic structure of FIG.3 (e.g., when a magnetoresistive element as shown in FIG. 7 is formed),as the thickness of the magnetic layer M11 increases, amagnetoresistance ratio (i.e., a MR ratio) of the magnetoresistiveelement may be increased. For example, the magnetoresistance ratio(i.e., the MR ratio) of the magnetoresistive element may be increased toabout 200%. Thus, if the magnetic structure according to exampleembodiments is used, a magnetoresistive element having excellentperformance may be obtained. If such a magnetoresistive element is usedin a memory device, an operation margin of the memory device may bewidened.

A structure of the upside-down flipped structure of FIG. 3 is possible.The example is shown in FIG. 4.

In FIG. 4, the magnetic layer M11 and the non-magnetic layer N10 aresequentially formed on the stress-inducing layer S10, and the magneticlayer M11 includes the first layer 10 and the second layer 20. Thesecond layer 20 is formed between the first layer 10 and thestress-inducing layer S10.

The magnetic structures of FIGS. 1 through 4 may further include asecond magnetic layer.

FIGS. 5 through 8 illustrate the cases in which the second magneticlayer is added to the magnetic structures of FIGS. 1 through 4.

Referring to FIGS. 5 through 8, the magnetic layers M10 and M11 may befirst magnetic layers M10 and M11, and the second magnetic layer M20 maybe further formed on a surface of the non-magnetic layer N10. The secondmagnetic layer M20 may be formed facing the first magnetic layer M10 orM11 with the non-magnetic layer N10 therebetween. Thus, the non-magneticlayer N10 may be formed between the first magnetic layer M10 or M11 andthe second magnetic layer M20. The second magnetic layer M20 may beformed of a ferromagnetic material including at least one of, forexample, Co, Fe, Ni and combinations thereof. The ferromagnetic materialmay further include an element other than Co, Fe, Ni and combinationsthereof, for example, B, Cr, Pt, Pd or combinations thereof. When thefirst magnetic layer M10 or M11 exhibits perpendicular magneticanisotropy, the second magnetic layer M20 may also exhibit perpendicularmagnetic anisotropy. However, a material of the second magnetic layerM20 is not limited thereto and may vary. Meanwhile, a thickness of thesecond magnetic layer M20 may be less than or equal to about 50 nm, forexample, less than or equal to about 30.

One of the first magnetic layer M10 or M11 and the second magnetic layerM20, for example, the first magnetic layer M10 or M11, may be a freelayer, and the other, for example, the second magnetic layer M20, may bea pinned layer. The free layer indicates a magnetic layer whosemagnetization direction may be changed, and the pinned layer indicates amagnetic layer whose magnetization direction is fixed (pinned). As themagnetization direction of the first magnetic layer M10 or M11 ischanged while the magnetization direction of the second magnetic layerM20 is pinned, resistance between the first magnetic layer M10 or M11and the second magnetic layer M20 may differ. Thus, the magneticstructure including the first magnetic layer M10 or M11, the secondmagnetic layer M20, and the non-magnetic layer N10 therebetween may be amagnetoresistive element. Particularly, when the non-magnetic layer N10is an insulating layer, the magnetoresistive element may be a magnetictunneling junction (MTJ) element. When the magnetization direction ofthe free layer (e.g., the first magnetic layer) is the same as themagnetization direction of the pinned layer (e.g., the second magneticlayer), the magnetoresistive element has a low value of resistance. Whenthe magnetization direction of the free layer (e.g., the first magneticlayer) is opposite to the magnetization direction of the pinned layer(e.g., the second magnetic layer), the magnetoresistive element has ahigh value of resistance. The low value of resistance of themagnetoresistive element may correspond to data ‘0,’ and the high valueof resistance may correspond to data ‘1’.

FIGS. 9A through 9E are cross-sectional views showing a method offorming the magnetic structure (the magnetoresistive element) accordingto example embodiments. The method according to the present exampleembodiments involves forming the magnetic structure (themagnetoresistive element) of FIG. 6.

Referring to FIG. 9A, a stress-inducing layer S100 may be formed on asubstrate (not shown). At this point, the stress-inducing layer S100 isnot a layer inducing stress in another layer, but will become “astress-inducing layer” later, and thus, is referred to as “astress-inducing layer” for convenience. The stress-inducing layer S100may be formed of a material with a thermal expansion coefficient greaterthan that of a magnetic layer (M100 of FIG. 9C) which will be formedlater. For example, the stress-inducing layer S100 may be formed of atleast one material selected from the group consisting of Al, Ga, Mn, Zn,Cu, etc. The stress-inducing layer S100 may be formed, for example, atroom temperature or at a temperature similar to room temperature (a lowtemperature of about 150° C. or less).

Referring to FIG. 9B, the stress-inducing layer S100 may be heated. Forexample, the stress-inducing layer S100 may be heated at a temperatureof about 200 to 500° C. In this regard, the stress-inducing layer S100may be expanded in the in-plane direction. When the stress-inducinglayer is formed on a substrate (not shown), the stress-inducing layerS100 may be heated by heating the substrate.

Referring to FIG. 9C, a first magnetic layer M100 and a non-magneticlayer N100 may be sequentially formed on the heated stress-inducinglayer S100. The first magnetic layer M100 may have IPMA at an interface(i.e., a contact surface) with the non-magnetic layer N100. In otherwords, a stacking structure of the first magnetic layer M100 and thenon-magnetic layer N100 may be an IPMA system or an IPMA structure. Thefirst magnetic layer M100 may include a Fe-based or CoFe-based material,and the CoFe-based material may include, for example, CoFeB. Thenon-magnetic layer N100 may include an oxide, for example, a Mg oxide(i.e., MgO). Because the first magnetic layer M100 and the non-magneticlayer N100 are formed while the stress-inducing layer S100 is heated,the first magnetic layer M100 and the non-magnetic layer N100 may bealso heated to the same (or to a similar) temperature as that of thestress-inducing layer S100.

Referring to FIG. 9D, the heated stress-inducing layer S100, the firstmagnetic layer M100, and non-magnetic layer N100 may be cooled to acertain temperature. For example, the layers S100, M100, and N100 may becooled to room temperature. Because the thermal expansion coefficient ofthe stress-inducing layer S100 is greater than that of the magneticlayer M100, a degree of contraction (shrinkage) of the stress-inducinglayer S100 in the in-plane direction may be greater than that of thefirst magnetic layer M100. Therefore, a compressive stress may beinduced in the first magnetic layer M100 in the in-plane direction dueto the stress-inducing layer S100. Thus, the first magnetic layer M100may have a lattice structure that is compressively strained due to thestress-inducing layer S100. Because a thickness of the first magneticlayer M100 is thin, the lattice structure may be compressively strainedin all region of the first magnetic layer M100. That is, as well as theregion of the first magnetic layer M10 which is in contact with thestress-inducing layer S100, the opposite region (i.e., the region of thefirst magnetic layer M100 which is in contact with the non-magneticlayer N100) may also be compressively strained. When the first magneticlayer M100 has a compressively strained structure, a magnetic anisotropyenergy of the first magnetic layer M100 may increase.

Referring to FIG. 9E, a second magnetic layer M200 may be formed on thenon-magnetic layer N100. The second magnetic layer M200 may be formed ofa ferromagnetic material including at least one of, for example, Co, Fe,and Ni. The ferromagnetic material may further include an element otherthan Co, Fe, and Ni, for example, B, Cr, Pt, or Pd. When the firstmagnetic layer M100 exhibits perpendicular magnetic anisotropy, thesecond magnetic layer M200 may also exhibit perpendicular magneticanisotropy. One of the first magnetic layer M100 and the second magneticlayer M200, for example the first magnetic layer M100, may be a freelayer, and the other, for example the second magnetic layer M200, may bea pinned layer. Such a magnetic structure of FIG. 9E may be amagnetoresistive element. When the non-magnetic layer N100 is aninsulating layer, the magnetic structure of FIG. 9E may be a MTJelement.

FIG. 10 is a flowchart summarizing the forming method described withreference to FIGS. 9A through 9E.

Referring to FIG. 10, a stress-inducing layer may be formed of amaterial with a high thermal expansion coefficient in a first step S1,the stress-inducing layer may be heated in a second step S2, and astacked structure of a first magnetic layer and a non-magnetic layer maybe formed thereon in a third step S3. Then, the stress-inducing layerand the stacked structure may be cooled in a fourth step S4, and asecond magnetic layer may be formed thereon in a fifth step S5. Thestacked structure of the first magnetic layer/the non-magnetic layerformed in the third step S3 may be an IPMA system. In the fourth step S4(i.e., a cooling step), a compressive stress may be applied to the firstmagnetic layer as the stress-inducing layer is contracted (shrunk) inthe in-plane direction. As a result, a lattice structure of the firstmagnetic layer may be compressively strained. The second magnetic layermay be formed at the third step S3 before the cooling stage (i.e., thefourth step S4). In other words, the cooling step S4 may be performedafter forming the second magnetic layer on the non-magnetic layer.

When the stress-inducing layer is formed of a material with the highthermal expansion coefficient, if the stress-inducing layer is depositedat a high temperature, a surface morphology of the stress-inducing layermay possibly be degraded. Particularly, when the material with a highthermal expansion coefficient is a metal, if depositing it at a hightemperature, the surface morphology of the stress-inducing layer maypossibly be degraded. However, according to example embodimentsdescribed above, the stress-inducing layer is first formed at roomtemperature or a temperature similar to room temperature, heated at alater stage, the first magnetic layer and the non-magnetic layer areformed thereon, and then the layers are cooled. Thus, theabove-mentioned problem, that is, degrading of the surface morphology ofthe stress-inducing layer may be prevented.

FIGS. 11A through 11D are cross-sectional views showing a method offorming a magnetic structure (a magnetoresistive element) according toexample embodiments. The method according to the present exampleembodiments involves forming the magnetic structure (themagnetoresistive element) of FIG. 5.

Referring to FIG. 11A, a second magnetic layer M201 may be formed. Thesecond magnetic layer M201 may be formed of a ferromagnetic materialincluding at least one of, for example, Co, Fe, Ni and combinationsthereof. The ferromagnetic material may further include an element otherthan Co, Fe, Ni or combinations thereof. The second magnetic layer M201may exhibit perpendicular magnetic anisotropy. A non-magnetic layer N101and a first magnetic layer M101 may be sequentially stacked on thesecond magnetic layer M201. The first magnetic layer M101 may have IPMAat an interface (i.e. contact surface) with the non-magnetic layer N101.The first magnetic layer M101 may include a Fe-based material or aCoFe-based material, and the CoFe-based material may include, forexample, CoFeB. The non-magnetic layer N101 may include an oxide, forexample, a Mg oxide (i.e., MgO).

Referring to FIG. 11B, the first magnetic layer M101, the non-magneticlayer N101, and the second magnetic layer M201 may be heated. Forexample, the layers M101, N101, and M201 may be heated to a temperatureof about 200 to 500° C. If the layers M101, N101, and M201 are formed ona substrate (not shown), the layers M101, N101, and M201 may be heatedby heating the substrate.

Referring to FIG. 11C, a stress-inducing layer S101 may be formed on thefirst magnetic layer M101 while the first magnetic layer M101, thenon-magnetic layer N101, and the second magnetic layer M201 are heated.The stress-inducing layer S101 may be formed of a material with athermal expansion coefficient greater than that of the first magneticlayer M101. For example, the stress-inducing layer S101 may be formed ofat least one material selected from the group consisting of Al, Ga, Mn,Zn, Cu, etc. Because the stress-inducing layer S101 is formed at a hightemperature, for example at about 200 to 500° C., the stress-inducinglayer S101 may be formed in an expanded form in the in-plane direction.

Referring to FIG. 11D, the stress-inducing layer S101, the firstmagnetic layer M101, the non-magnetic layer N101, and the secondmagnetic layer M201 may be cooled to a certain temperature. For example,the layers S101, M101, N101, and M201 may be cooled to room temperature.Because the thermal expansion coefficient of the stress-inducing layerS101 is greater than that of the first magnetic layer M101, a degree ofcontraction (shrinkage) of the stress-inducing layer S101 in thein-plane direction may be greater than that of the first magnetic layerM101. Therefore, a compressive stress may be applied to the firstmagnetic layer M101 in the in-plane direction due to the stress-inducinglayer S101. Thus, the first magnetic layer M101 may have a latticestructure that is compressively strained due to the stress-inducinglayer S101.

FIG. 12 is a flowchart summarizing the forming method described withreference to FIGS. 11A through 11D.

Referring to FIG. 12, a stacked structure of a non-magnetic layer and afirst magnetic layer may be formed on a second magnetic layer in a firststep S11, and the layers may be heating to a certain temperature of, forexample, about 200 to 500° C. in a second step S21. Then, astress-inducing layer may be formed of a material with a high thermalexpansion coefficient on the heated first magnetic layer in a third stepS31, the stress-inducing layer and the stacked structure may be cooledin a fourth step S41. In the fourth step S41 (i.e., a cooling step), acompressive stress may be applied to the first magnetic layer as thestress-inducing layer is contracted (shrunk) in the in-plane direction.As a result, a lattice structure of the first magnetic layer may becompressively strained.

FIGS. 13A through 13D are cross-sectional views showing a method offorming a magnetic structure (a magnetoresistive element) according toexample embodiments. The method according to the present exampleembodiments involves forming the magnetic structure (themagnetoresistive element) of FIG. 6.

Referring to FIG. 13A, a stress-inducing layer S102 may be formed on asubstrate (not shown). At this stage, the stress-inducing layer S102 isnot a layer inducing stress in another layer, but will become “astress-inducing layer” later, and thus, is referred to as “astress-inducing layer” for convenience. The stress-inducing layer S102may be formed of a phase transformation material. The phasetransformation material may be a material that has a first phase at lowtemperature and has a second phase at high temperature. A latticeparameter of the second phase in the in-plane direction may be smallerthan that of the first phase. The phase transformation material may be amaterial which transforms to the second phase at high temperature andcontinuously maintains the second phase even when the temperature isdecreased to a low temperature. That is, the phase transformationmaterial may be a material that transforms its phase irreversibly. Atthis stage, the stress-inducing layer S102 may have the first phase. Forexample, the phase transformation material may include MnAl. Here, theMnAl may have ε′-phase as illustrated in FIG. 20A. The ε′-phase of FIG.20A may correspond to the first phase.

Referring to FIG. 13B, a first magnetic layer M102 and a non-magneticlayer N102 may be sequentially formed on the stress-inducing layer S102.The first magnetic layer M102 may have IPMA at an interface (i.e.contact surface) with the non-magnetic layer N102. In other words, thefirst magnetic layer M102 and the non-magnetic layer N102 may form anIPMA system or an IPMA structure. The first magnetic layer M102 mayinclude a Fe-based or CoFe-based material, and the CoFe-based materialmay include, for example, CoFeB. The non-magnetic layer N102 may includean oxide, for example, a Mg oxide (i.e., MgO).

Referring to FIG. 13C, a phase of the stress-inducing layer S102 may bechanged (transformed). A stage of changing (transforming) the phase ofthe stress-inducing layer S102 may include heating the stress-inducinglayer S102 to a given temperature (e.g., about 300° C. or higher). Asthe phase of the stress-inducing layer S102 changes to a second phase,the lattice parameter of the stress-inducing layer S102 in the in-planedirection may be contracted. Thus, a compressive stress may be appliedto the first magnetic layer M102 in the in-plane direction due to thestress-inducing layer S102. Therefore, the first magnetic layer M102 mayhave a lattice structure that is compressively strained due to thestress-inducing layer S102. Because a thickness of the first magneticlayer M102 is thin, the lattice structure may be compressively strainedin an overall area of the first magnetic layer M102. When the firstmagnetic layer M102 has a compressively strained structure, a magneticanisotropy energy of the first magnetic layer M102 may increase.

For example, when the stress-inducing layer S102 of FIG. 13C includesMnAl as a phase transformation material, the phase of MnAl may transformfrom ε′-phase of FIG. 20A to τ-phase of FIG. 20B. The τ-phase of FIG.20B may correspond to the second phase. Parameter b′ in τ-phase of FIG.20B is smaller than parameter b in ε′-phase of FIG. 20A. That is, thelattice parameter in the in-plane direction is contracted due to thephase transformation.

Referring to FIG. 13D, a second magnetic layer M202 may be formed on thenon-magnetic layer N102. The second magnetic layer M202 may be formed ofa ferromagnetic material including at least one of, for example, Co, Fe,Ni and combinations thereof. The ferromagnetic material may furtherinclude an element other than Co, Fe, Ni and combinations thereof. Whenthe first magnetic layer M102 exhibits perpendicular magneticanisotropy, the second magnetic layer M202 may also exhibitsperpendicular magnetic anisotropy. One of the first magnetic layer M102and the second magnetic layer M202, for example the first magnetic layerM102, may be a free layer, and the other, for example the secondmagnetic layer M202, may be a pinned layer. Such a magnetic structure ofFIG. 13D may be a magnetoresistive element. When the non-magnetic layerN102 is an insulating layer, the magnetic structure of FIG. 13D may be aMTJ element.

FIG. 14 is a flowchart summarizing the forming method described withreference to FIGS. 13A through 13D.

Referring to FIG. 14, a stress-inducing layer including a phasetransformation material may be formed in a first step S12, a stackedstructure of a first magnetic layer and a non-magnetic layer may beformed thereon in a second step S22. Next, a phase of thestress-inducing layer may be transformed in a third step S32, and asecond magnetic layer may be formed on the non-magnetic layer in afourth step S42. The stacked structure of the first magnetic layer andthe non-magnetic layer formed in the second step S22 may be an IPMAsystem. In a third step S32 (i.e., a phase transforming step),compressive stress may be applied to the first magnetic layer as thestress-inducing layer contracts in the in-plane direction. As a result,a lattice structure of the first magnetic layer may be compressivelystrained. The second magnetic layer may be formed at the second step S22before the phase transforming step (i.e., the third step) S32. In otherwords, the phase transforming step S32 may be performed after formingthe second magnetic layer on the non-magnetic layer.

FIGS. 15A through 15D are cross-sectional views showing a method offorming a magnetic structure (a magnetoresistive element) according toexample embodiments. The method according to example embodimentsinvolves forming the magnetic structure (the magnetoresistive element)of FIG. 5.

Referring to FIG. 15A, a second magnetic layer M203 may be formed. Thesecond magnetic layer M203 may be formed of a ferromagnetic materialincluding at least one of, for example, Co, Fe, Ni and combinationsthereof. The ferromagnetic material may further include an element otherthan Co, Fe, Ni or combinations thereof. The second magnetic layer M203may exhibit perpendicular magnetic anisotropy. Then, a non-magneticlayer N103 and a first magnetic layer M103 may be sequentially stackedon the second magnetic layer M203. The first magnetic layer M103 mayhave IPMA at an interface (i.e. contact surface) with the non-magneticlayer N103. The first magnetic layer M103 may include a Fe-based orCoFe-based material, and the CoFe-based material may include, forexample, CoFeB. The non-magnetic layer N103 may include an oxide, forexample, a Mg oxide (i.e., MgO).

Referring to FIG. 15B, a stress-inducing layer S103 may be formed on thefirst magnetic layer M103. At this stage, the stress-inducing layer S103is not a layer that induces stress in the first magnetic layer M103, butwill become “a stress-inducing layer” later, and thus, is referred to as“a stress-inducing layer” for convenience. The stress-inducing layerS103 may be formed of a phase transformation material. The phasetransformation material may be the same material as described above inrelation to FIG. 13A.

Referring to 15C, a phase of the stress-inducing layer S103 may bechanged (transformed). A method of changing (transforming) the phase ofthe stress-inducing layer S103 may be either identical or similar to themethod of changing (transforming) the phase as described above inrelation to FIG. 13C. As the phase of the stress-inducing layer S103changes (transforms), the lattice parameter of the stress-inducing layerS103 in the in-plane direction may be contracted, and thus a compressivestress may be applied to the first magnetic layer M103 in the in-planedirection. Therefore, the first magnetic layer M103 may have a latticestructure that is compressively strained due to the stress-inducinglayer S103.

FIG. 16 is a flowchart summarizing the forming method described withreference to FIGS. 15A through 15C.

Referring to FIG. 16, a staked structure of a non-magnetic layer and afirst magnetic layer may be formed on a second magnetic layer in a firststep S13, a stress-inducing layer including a phase transformationmaterial may be formed on the first magnetic layer in a second step S23,and a phase of the stress-inducing layer may be changed (transformed) ina third step S33. In the third step S33 (i.e., a phase transformingstep), a compressive stress may be applied to the first magnetic layeras the stress-inducing layer contracts in the in-plane direction. As aresult, a lattice structure of the first magnetic layer may becompressively strained.

According to example embodiments, in order to induce the compressivestrain of a magnetic layer, a stress-inducing layer may be formed of amaterial with a lattice parameter smaller than that of the magneticlayer. The lattice parameter of the stress-inducing layer in thein-plane direction may be smaller than that of the magnetic layer. Adifference between the lattice parameter of the stress-inducing layerand the lattice parameter of the magnetic layer may be within about 10%.If the material with the lattice parameter that is smaller than that ofthe magnetic layer is in contact with the magnetic layer, a compressivestress may be applied to the magnetic layer. Considering a situation ofepitaxial growth, when the magnetic layer is epitaxially grown on amaterial layer with a relatively smaller lattice parameter, acompressive stress may be applied to the magnetic layer due to thematerial layer with the relatively smaller lattice parameter. Byapplying the material with the lattice parameter that is smaller thanthat of the magnetic layer as a material of the stress-inducing layer, amagnetic structure (a magnetoresistive element) as in FIG. 5 or FIG. 6may be formed.

Also, according to example embodiments, the first magnetic layer M100,M101, M102, or M103 used in various manufacturing methods describedabove may be formed of a multi-layer structure. For example, the firstmagnetic layer M100, M101, M102, or M103 may be formed of a double-layerstructure including the first layer (10 of FIG. 7 or FIG. 8) and thesecond layer (20 of FIG. 7 or FIG. 8). Here, the second layer mayinclude a material with saturation magnetization (Ms) smaller than thatof the first layer. As such, if the first magnetic layer M100, M101,M102, or M103 is formed of a multi-layer structure, a magnetic structure(a magnetoresistive element) as in FIG. 7 or FIG. 8 may be manufactured.In addition, the manufacturing methods described above may be modifiedin various ways.

The magnetic structure (the magnetoresistive element) according toexample embodiments may be used in various magnetic devices andelectronic devices. For example, the magnetic structure (themagnetoresistive element) may be used in a memory cell of a memorydevice. As explained above, the magnetic structure (the magnetoresistiveelement) according to example embodiments may be easily scaled down andmay have excellent performance and thermal stability, and thus if usedin a memory device, a memory device of high density/high performance maybe manufactured. The magnetoresistive element according to exampleembodiments may be used in many other devices as well as in the memorydevice.

FIG. 17 is a view showing an example of a memory device including amagnetic structure (a magnetoresistive element) according to exampleembodiments.

Referring to FIG. 17, the memory device according to the present exampleembodiments may include a magnetoresistive element MR1 and a switchingelement TR1 connected thereto in a memory cell MC1. The magnetoresistiveelement MR1 may include one of the various structures described in FIGS.5 through 8, for example, the structure of FIG. 6. One of a firstmagnetic layer M10 and a second magnetic layer M20 of themagnetoresistive element MR1, for example the first magnetic layer M10,may be a free layer, and the other, for example the second magneticlayer M20, may be a pinned layer. The switching element TR1 may be, forexample, a transistor. The switching element TR1 may be electricallyconnected to the first magnetic layer M10 of the magnetoresistiveelement MR1.

The memory cell MC1 may be connected between a bit-line BL1 and aword-line WL1. The bit-line BL1 and the word-line WL1 may be formed tointersect each other, and the memory cell MC1 may be formed at the pointof intersection. The bit-line BL1 may be connected to themagnetoresistive element MR1. The second magnetic layer M20 of themagnetoresistive element MR1 may be electrically connected to thebit-line BL1. The word-line WL1 may be connected to the switchingelement TR1. When the switching element TR1 is a transistor, theword-line WL1 may be connected to a gate electrode of the switchingelement TR1. A write current, a read current, an erase current, etc. maybe applied to the memory cell MC1 via the word-line WL1 and the bit-lineBL1.

Although one memory cell MC1 is shown in FIG. 17, a plurality of thememory cells MC1 may be arranged to form an array. That is, a pluralityof the bit-lines BL1 and a plurality of the word-lines WL1 may bearranged intersecting each other, and the memory cell MC1 may bedisposed at each point of intersection.

The memory device of FIG. 17 may be a magnetic random access memory(MRAM). Here, the memory device of FIG. 17 may be a device that writesdata by using a spin transfer torque. The spin transfer torque may beinduced by a current. As a spin torque induced by the current istransferred to the free layer, for example the first magnetic layer M10,the first magnetic layer M10 may be magnetized in a given direction.According to a direction of the current, a magnetization direction ofthe first magnetic layer M10 may differ. The memory device that writesdata by using the spin transfer torque may be referred to as a spintransfer torque MRAM (STT-MRAM). In a case of STT-MRAM, an additionalwire (i.e., a digit line) to generate an external magnetic field is notnecessary unlike a conventional MRAM, and thus the STT-MRAM may behighly integrated and may be simply operated.

While aspects have been particularly shown and described with referenceto differing elements thereof, it should be understood that the exampleembodiments described herein should be considered in a descriptive senseonly and not for purposes of limitation. For example, it may be obviousto one of ordinary skill in the art to which example embodiments arerelated that the magnetic structures (the magnetoresistive elements) ofFIGS. 1 through 8 may be modified in various ways. As a concreteexample, a second stress-inducing layer in contact with the secondmagnetic layer M20 may be further included in the magnetic structures(the magnetoresistive elements) of FIGS. 5 through 8, and here, thesecond magnetic layer M20 may also have a lattice structure that iscompressively strained. Also, the magnetic structures (themagnetoresistive elements) according to example embodiments may be usedin memory devices of other structure as well as the memory device ofFIG. 17 or in other magnetic devices (e.g., a magnetic sensor etc.)rather than the memory devices. In addition, the methods of forming themagnetic structures (the magnetoresistive elements) described inreference to FIGS. 9A through 16 may be changed in various ways.Therefore, the scope is defined not by the detailed description but bythe appended claims.

What is claimed is:
 1. A magnetic structure, comprising: a magneticlayer; a stress-inducing layer on a first surface of the magnetic layer;and a non-magnetic layer on a second surface of the magnetic layer,wherein the stress-inducing layer is configured to induce a compressivestress in the magnetic layer, and the magnetic layer has a latticestructure compressively strained due to the stress-inducing layer. 2.The magnetic structure of claim 1, wherein the magnetic layer hasinterface perpendicular magnetic anisotropy (IPMA) due to an interfacebetween the magnetic layer and the non-magnetic layer.
 3. The magneticstructure of claim 1, wherein the magnetic layer includes a Fe-basedmaterial or a CoFe-based material.
 4. The magnetic structure of claim 3,wherein the CoFe-based material includes CoFeB.
 5. The magneticstructure of claim 1, wherein the non-magnetic layer includes an oxide.6. The magnetic structure of claim 5, wherein the oxide includes amagnesium (Mg) oxide.
 7. The magnetic structure of claim 1, wherein thestress-inducing layer includes a material with a thermal expansioncoefficient higher than a thermal expansion coefficient of the magneticlayer.
 8. The magnetic structure of claim 7, wherein the stress-inducinglayer includes at least one of Al, Ga, Mn, Zn, Cu and combinationsthereof.
 9. The magnetic structure of claim 1, wherein thestress-inducing layer include a phase transformation material.
 10. Themagnetic structure of claim 1, wherein the stress-inducing layerincludes a material with a lattice parameter smaller than a latticeparameter of the magnetic layer.
 11. The magnetic structure of claim 1,wherein the magnetic layer is between the stress-inducing layer and thenon-magnetic layer.
 12. The magnetic structure of claim 1, wherein themagnetic layer includes, a first layer in contact with the non-magneticlayer; and a second layer between the first layer and thestress-inducing layer, wherein a saturation magnetization (Ms) of thesecond layer is smaller than a saturation magnetization of the firstlayer.
 13. The magnetic structure of claim 12, wherein the magneticlayer has a thickness of about 1 nm to about 3 nm.
 14. The magneticstructure of claim 1, wherein the magnetic layer is a first magneticlayer, the magnetic structure further comprises a second magnetic layeron a surface of the non-magnetic layer, and the non-magnetic layer isbetween the first magnetic layer and the second magnetic layer.
 15. Themagnetic structure of claim 14, wherein one of the first and secondmagnetic layers is a free layer, and the other is a pinned layer. 16.The magnetic structure of claim 14, wherein the magnetic structure is amagnetoresistive element.
 17. A method of forming a magnetic structure,the method comprising: forming a magnetic layer having a latticestructure compressively strained due to a stress-inducing layer; andforming a non-magnetic layer contacting the magnetic layer.
 18. Themethod of claim 17, wherein the magnetic layer has interfaceperpendicular magnetic anisotropy (IPMA) due to an interface between themagnetic layer and the non-magnetic layer.
 19. The method of claim 17,wherein the stress-inducing layer is formed of a material with a thermalexpansion coefficient higher than a thermal expansion coefficient of themagnetic layer.
 20. The method of claim 19, wherein forming the magneticlayer includes, heating the stress-inducing layer; forming a magneticmaterial layer on the heated stress-inducing layer; and cooling themagnetic material layer and the stress-inducing layer such that thelattice structure of the magnetic material layer is compressivelystrained and the magnetic layer is formed.
 21. The method of claim 19,wherein forming the magnetic layer includes, forming a magnetic materiallayer; heating the magnetic material layer; forming the stress-inducinglayer on the heated magnetic material layer; and cooling thestress-inducing layer and the magnetic material layer such that thelattice structure of the magnetic material layer is compressivelystrained and the magnetic layer is formed.
 22. The method of claim 17,wherein the stress-inducing layer is formed of a phase transformationmaterial.
 23. The method of claim 22, wherein forming the magnetic layerincludes, forming the stress-inducing layer and a magnetic materiallayer in contact with the stress-inducing layer; and changing a phase ofthe stress-inducing layer such that the lattice structure of themagnetic material layer is compressively strained.
 24. The method ofclaim 17, wherein the stress-inducing layer is formed of a material witha lattice parameter smaller than a lattice parameter of the magneticlayer.
 25. The method of claim 17, wherein the magnetic layer includes,a first layer in contact with the non-magnetic layer; and a second layerdisposed between the first layer and the stress-inducing layer, andwherein a saturation magnetization (Ms) of the second layer is smallerthan a saturation magnetization of the first layer.
 26. The method ofclaim 17, wherein the magnetic layer is a first magnetic layer, themethod further comprises forming a second magnetic layer on a surface ofthe non-magnetic layer, and the non-magnetic layer is disposed betweenthe first and second magnetic layer.
 27. The method of claim 26, whereinone of the first and second magnetic layers is a free layer, and theother is a pinned layer.
 28. A memory device, comprising: at least onememory cell including a magnetoresistive element, wherein themagnetoresistive element includes, first and second magnetic layersspaced apart from each other, a non-magnetic layer between the first andsecond magnetic layers, and a stress-inducing layer configured to inducea compressive stress in the first magnetic layer, wherein the firstmagnetic layer has a lattice structure compressively strained due to thestress-inducing layer.
 29. The memory device of claim 28, wherein thememory cell further includes a switching element connected to themagnetoresistive element.
 30. The memory device of claim 28, wherein thefirst magnetic layer is a free layer, and the second magnetic layer is apinned layer.
 31. The memory device of claim 28, wherein the firstmagnetic layer has interface perpendicular magnetic anisotropy (IPMA)due to an interface between the first magnetic layer and thenon-magnetic layer.
 32. The memory device of claim 28, wherein thestress-inducing layer includes a material with a thermal expansioncoefficient higher than a thermal expansion coefficient of the firstmagnetic layer.
 33. The memory device of claim 28, wherein thestress-inducing layer includes a phase transformation material.
 34. Thememory device of claim 28, wherein the stress-inducing layer includes amaterial with a lattice parameter smaller than a lattice parameter ofthe first magnetic layer.
 35. The memory device of claim 28, wherein thefirst magnetic layer includes, a first layer in contact with thenon-magnetic layer; and a second layer disposed between the first layerand the stress-inducing layer, wherein a saturation magnetization (Ms)of the second layer is smaller than a saturation magnetization of thefirst layer.
 36. The memory device of claim 28, wherein the memorydevice is a spin transfer torque magnetic random access memory(STT-MRAM).